The present invention relates to automated sheet feeder apparatus for scanning equipment and the like, and more particularly to a configuration that facilitates document separation and spacing for use with universal document feeder apparatus associated with high-speed image scanning equipment requiring high-volume document throughput.
Automated high-speed image scanning equipment utilizes an imaging device to scan the images from an input or source document. Such equipment must feed and transport documents to the imaging device quickly, smoothly, and automatically, and must be trouble-free. The feeding equipment must quickly and smoothly feed each original document or individual sheet from the backlog queue of input or source documents waiting to be scanned to the transport apparatus. The transport apparatus then brings each document or sheet to the imaging device. To achieve high-volume throughput, the high-volume feeder apparatus must be able to supply the individual documents or sheets in a spaced relationship to the input section of the transport apparatus in a manner that is completely reliable and trouble-free.
A problem associated with high-speed image scanning equipment found in the prior art is that the individual source or input documents commonly are not standardized. They vary in shape and size, and come in a variety of different thicknesses (e.g., sheets ranging from an onionskin thickness to thick card stock). This mandates that each non-uniform document be processed or handled in a uniform manner.
Another related problem is that, in the majority of instances, the input or source document is an original document or a document that is not easily replaced. It becomes imperative that the document feed mechanism not damage any of the source documents under any circumstances.
A persistent problem found in the prior art is the more or less random feeding of multiple documents at one time by the document feed mechanism, rather than a single sheet. The problem is commonly referred to, by those skilled in the art, as the "multi-feeds" problem. The multi-feeds problem is made even more critical when a high-volume document throughput is required for high-speed image scanning equipment and the like. In such situations, the individual source documents waiting to be scanned are in a stack, and either the top or bottom document is fed sequentially to the image scanner by the document feed mechanism. A number of variables are supposedly responsible for this negative result, including but not limited to the weight of the skimmer roller assembly (which rests on top of the first document in the stack of documents waiting to be scanned), the underlying dynamics of the friction that the bottom and top sheets experience as the document feed mechanism accelerates the next sheet from the stack forward, and the spacing required between individual documents as documents enter the document feed mechanism and are sequentially processed.
Yet another common problem with certain document feed mechanisms for high-speed image scanning equipment and the like found in the prior art is that, over time, this equipment will occasionally cause bottlenecks and/or jam-ups of downstream equipment, having an obvious negative effect on overall document throughput. Sometimes the problem can be corrected by timely maintenance of the document feed mechanism. High-speed image scanning equipment that provides for high-volume document throughput necessitates a reliable document feed mechanism that is easy to maintain and is capable of fulfilling document throughput requirements.
A particular prior device currently in use employs a relatively narrow skimmer roller at the entrance to the feeder together with an adjustable separate weight that causes the skimmer roller to grip the paper. The prior device also uses a pair of counter-rotating shafts with interleaved roller portions that are designed to advance the top page while retarding any adjacent or lower pages. Finally, in that device there is space between the skimmer roller and the interleaved forwarding and reversing rollers. Sheets being fed sometimes buckle or bunch up in that space. The counterrotating shafts are set an adjustable distance apart. The inventors have found that this arrangement results in paper jams and multifeeds when stacks of documents with different thicknesses are introduced.
Another prior commercial device utilizes a driven advancing roller nipped with a retarding roller coupled by a brake assembly to a fixed shaft. The advancing roller urges one face of the sheet forward, while the retarding roller acts as a drag on the opposite face of the sheet. If multiple sheets pass between the advancing and the retarding rollers, the advancing roller will urge the first sheet forward and the retarding roller will drag on the other sheet. Since the friction between the retarding roller and the sheet is higher than the friction between two sheets, the retarding roller will prevent the passing of the lower sheet. While this is not a "reversing" roller per se, but rather a simple "drag" on the lower of two adjacent sheets, it tends to separate the two while the upper sheet passes through the gap under the drive of the advancing roller. The inventors have found that this invention, however, could not resolve the problem of multi-feed of three or more sheets at a time.
Also in the prior art are various arrangements for the retarding roller. The first of these is an earlier development in which a retarding roller is mounted on a fixed shaft and has a peripheral rubber surface that frictionally engages the peripheral outer surface of the advancing roller or the sheet between the rollers. A tubular coil spring is attached at one end to the retarding roller and wrapped around the fixed shaft. When the advancing roller moves in the forward direction, the friction between the outer surfaces of the retarding and advancing rollers urges the retarding roller forward, thus tending to turn the coil spring on the fixed shaft. This torsional motion tensions the coil spring and reduces its diameter. The coil spring constricts about the fixed shaft, acting as a brake. When more than one sheet is passed between the rollers, the advancing roller pushes the top sheet in the forward direction. The retarding roller is uncoupled from the advancing roller, as the two or more feed sheets between the advancing and retarding rollers slip relative to each other. Uncoupling the rollers allows the spring to unwind. The unwinding spring momentarily turns the retarding roll backward for about one revolution. An example of this mechanism can be found in Bell & Howell's Scanner Model No. 0101276 and 0101300. This arrangement can correct the misfeeding of two sheets but not necessarily a stack of three or more misfed sheets. The reverse rotation or recoil of the retarding roller is limited, so the retarding effect is limited too.